Modular competitiveness for distributed algorithms

Modular Competitiveness for Distributed Algorithms James Aspnes” Orli Waartst We define a novel measure of competitive performance for distributed algorithms based on throughput, the number of tasks that an a3gorithm can carry out in a fixed amount of work. An important property of the throughput measure is that it is modular: we define a notion of relative competitiveness with the property that a k-relatively competitive implementation of an object T using a subroutine U, combined with an l-competitive implement ation of U, gives a M-competitive algorithm for T. We prove the throughput-competitiveness of an algorithm for a fundamental building block of many well-known distributed algorithms: the cooperative collect primitive. ThE permits a straightforward construction of competitive versions of these algorithms— the first examples of algorithms obtained through a general method for modular construction of competitive distributed algorithms. Moreover, we provide a lower bound that shows that the throughput competitiveness of the cooperative collect algorithm we study is nearly optimal Thus, we see our paper aa making two main contributions: one is the introduction of a modular measurement for competitiveness, whose interest is justified by the throughput competitiveness of the cooperative collect algorithms; and the other is a technique for proving throughput competitiveness, which may apply to other distributed problems. ● Yale University, Department of Computer Science, 51 Prospect Street/P.O. Box 208285, New Haven CT 06520-8285. Supported by NSF grants CCR9410228 and CCR941541O. E mail: a.spnes-jsaes@cs. yala .eda tcomputer science Division, U. C. Berkeley. sup ported in part by an NSF postdoctoral fellowship. EMail: waartsacs. berkalay. edn Permission to make digital/hard copies of all or part of tbk material for persons] or claaaroom use is granted without fee provided that the copies are not made or dktributed for profit or conunemial advantage, the copyright notice, the title of the publication and its date appear, and notice is given that copyright is by permission of the ACM, Ioc. To copy otherwise, to republish, to poet on servera or to redistribute to lists, requires specific pennisaion and/or fee. STOC’96, Philadelphia PA, USA e 1996 ACM 0-89791-785-5/96/05. .$3.50